1. Field of the Invention
The present invention relates to locks and more particularly to an apparatus for and method of rekeying a pin tumbler cylinder lock having tumbler pins, driver pins and at least one master pin without disassembly of the lock apparatus or removal or replacement of any master pins therefrom or therein.
2. Description of the Prior Art
The pin tumbler lock principle is widely used in builders hardware locks, padlocks and cabinet locks. A pin tumbler lock housing has a cylindrical main bore extending longitudinally therethrough to rotatably accommodate a cylindrical plug having a flange at its front end to limit its rearward movement relative to the housing. The plug has a keyway extending longitudinally therethrough at the bottom of the plug. A plurality of parallel and equally spaced cylindrical top pinways extend perpendicular to the main bore from the top of the housing into the main bore to align with correspondingly spaced cylindrical bottom pinways extending from the top of the plug to part way into the keyway. Retainers of various types secured to the rear end of the plug provide a minimum of end play between the plug and the housing when the lock is assembled. Each pinway extending from the top of the housing to part way into the keyway has within it a tumbler pin having a truncated conical bottom end that engages a truncated cut or bitting on the top edge of a key inserted in the keyway. The bitting positions the tumbler pin vertically in the pinway. Above each tumbler pin is a driver pin of sufficient height to block a shear interface between the plug and the housing when the tumbler and driver pins are bottomed in their pinway. Above each driver pin is a compression spring that biases the driver pin and the tumbler pin in a downward direction. The height of a tumbler pin is such that the interface between the tumbler pin and the driver pin is located at the shear interface by a properly selected bitting on a key inserted in the keyway. When the key bittings locate all such driver pin and tumbler pin interfaces at the shear interface, the plug is free to rotate and retract a bolt or latch by means of the surfaces of the retainer, or an extension thereof, acting on the bolt or latch.
Tumbler pin heights and bitting depths of the key are multiples of an increment established by the manufacturer. There are usually ten tumbler pin heights and ten corresponding bitting depths numbered zero through nine, zero designating the shortest tumbler and the shallowest bitting depth and nine designating the tallest tumbler and the deepest bitting depth. The increment is large enough to ensure that a key having one or more bitting depths shallower or deeper than corresponding tumblers will not permit the plug to rotate because of the normal clearance between the plug and the housing.
A key that is intended for use with an individual lock or a group of locks keyed alike is referred to as a change key. A key that will operate a group of locks, each of which is operated by its own unique change key, is referred to as a master key. Pin tumbler locks are masterkeyed by using short pins called master pins between the tumbler pin and the driver pin in a given pinway. A tumbler pin, a driver pin and any master pins between them can be referred to as a tumbler stack. The interface between a master pin and a driver pin usually determines the change key bitting. The interface between the tumbler pin and the master pin usually determines the master key bitting. A plurality of locks can thus be set up to each operate only with its own unique change key, yet all of the locks can be operated with the same master key.
For ease of reference, the locations of the pinways, and thus the locations of the bittings for operating the tumbler stack in the respective pinways, are referred to as stations designated by the letters A, B, C, etc., with station A relating to the pinway that is closest to the front of the lock.
The necessity to re-key locks is an ongoing problem, particularly with a turnover of employees and tenants. Some concerns, such as banks, consider re-keying on a periodic basis to be a matter of good policy. Normally, re-keying for a different unique change key of a lock requires disassembly of the lock and removal and replacement of tumbler pins with tumbler pins of different heights if the lock is not masterkeyed. If masterkeyed, removal and replacement with different-height master pins has been required. Ideally, the delay in waiting for and the expense of a locksmith are to be avoided.
Attempts have been made to remove a temporary pin from a lock so that the lock cannot be operated by a temporary key. The temporary pin is provided in one of the pinways. When the removable temporary pin is removed from such lock, the original temporary key is no longer usable to operate the lock because the driver pin extends across the shear interface when the temporary key is used. In such lock, a disabling key is bitted such that the driver pin-tumbler pin interfaces of the pins in the pinways that do not have removable pins are aligned with the shear interface. Also, the removable temporary pin is in the top pinway with the bottom thereof aligned with the shear interface. The disabling key is thus enabled to rotate the plug so that a cut in the bottom of the disabling key is positioned under the top pinway. The keyway is enlarged to allow the removable pin to move into the cut and, as the disabling key is removed from the lock, to allow the removable pin to be pulled completely out of the lock. Such locks could provide re-keying by requiring use of many different change keys only to the extent that many removable temporary pins are provided when the lock is originally assembled. Such requirement for many removable pins to enable use of many different change keys is inherently disadvantageous since the more master pins (e.g. the removable pins) there are in the tumbler stacks, the easier the lock is to pick.
Later attempts to overcome such disadvantage used similar removable master pins and disabling keys to remove such master pins from the lock. Once the removable master pin was removed from the lock, a new removable master pin was loaded into a cut formed in a second re-keying key provided with a leaf spring biased by the removable master pin in the cut. With the new removable master pin held in the cut against the bias of the leaf spring, the second re-keying key was inserted into the keyway. The second key was bitted to operate the lock to allow rotation of the key and plug and positioning of the spring biased new master pin opposite to a desired top pinway. The leaf spring urged the new master pin into the top pinway against the action of the compression spring. Although such second key enabled the replacement of a new master pin into the lock, problems arose in attempting to hold the new master pin in the slot against the action of the leaf spring while inserting the second key and the new master pin into the keyway. Moreover, since the bias of the leaf spring must be greater than that of the compression spring to allow the new master pin to be pushed into the top pinway, the second key cannot be used to remove the removable master pin from the original pinway. Thus, two keys are required to successively remove a master pin from the lock and add a new master pin to the lock. Further, the requirement that the leaf spring act against the bias of the compression spring to push the new master pin into the pinway doesn't provide any positive assurance that the new pin has actually entered the pinway.
Improvements in such locks have been directed to assuring that the removable pins fit loosely in the cut in the first re-keying key and to preventing the driver pins from entering the cut by making the diameter of the cut and the removable pins less than that of the driver pin.
Locks have generally been keyed for operation using many keys, including, for example, a key for use only during construction. The removal of the master pin prevents use of the construction key with the lock, while all of the rest of the original keys can operate the lock. However, the re-keying keys and the structure of the lock do not render the lock usable with only one of the many keys instead of the construction key that is locked-out.
Independent of these efforts to provide a re-keyable lock, in one prior lock a slot was provided in the plug for receiving a slide having eight holes for use with four pinways. When the lock was assembled, the extra or auxiliary holes were either empty, filled with master pins having a height that was equal to the full thickness of the slide or filled with master pins that were shorter than the full thickness of the slide. A set screw was used to move the slide in the slot into one of two positions to align two different sets of the holes with the pinways. Because of the different arrangement of holes and master pins in each of the two positions of the slide, a different change key was required to operate the lock for each position of the slide. However, without increasing the length of the lock, or disassembling the lock, the lock could be re-keyed for only two change keys. Further, because of the variable thickness master pins and empty holes, once the slide was moved to the rear of the lock, the lock had to be disassembled to move the slide forward to re-key the lock.